Home > Concepts, Ephemeris Program, Observing, The Moon > Ephemeris: 07/24/2023 – The Moon appears to wobble a bit

Ephemeris: 07/24/2023 – The Moon appears to wobble a bit

July 24, 2023

This is Ephemeris for Monday, July 24th. Today the Sun will be up for 14 hours and 57 minutes, setting at 9:17, and it will rise tomorrow at 6:21. The Moon, 1 day before first quarter, will set at 12:24 tomorrow morning.

The Moon tonight is nearly half illuminated. In binoculars the dark oval spot visible on the Moon’s right edge is the Sea of Crises or Mare Crisium a small dark lava plain. The Moon’s rotation is quite uniform, however its orbit isn’t circular, so the Moon’s motion in its orbit slows as it moves farthest from the Earth, called apogee, and is sped up when closest, at perigee, So its face seems to rock a bit back and forth over the month. It’s an effect called libration. And one way to track that is to note how close the Mare Crisium (Sea of Crises) is to the edge of the Moon. It appears close to the right edge now. A week from now, that sea will appear to move away from the edge. Unfortunately, by then the Moon will be full, and night will soon fall on that little sea.

The astronomical event times given are for the Traverse City/Interlochen area of Michigan (EDT, UT –4 hours). They may be different for your location.

Addendum

The Moon on two dates 8 days apart, showing the apparent wobble or libration of the Moon by the changing position of Mare Crisium (Sea of Crises). Also note that the full moon is larger. It’s a supermoon, for what it’s worth. Created using Virtual Moon Atlas, LibreOffice Draw, and GIMP.
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